Evidence of Sumo Bout Fixing

The evidence was found in e-mails on 13 wrestlers’ mobile phones, seized by the Metropolitan Police Department (MPD) in its ongoing gambling investigation. About 50 e-mail exchanges from March through June last year indicate that the wrestlers bought and sold victories for sums in the hundreds of thousands of yen, as well as traded victories and losses from tournament to tournament — evidence directly at odds with the Japan Sumo Association (JSA)’s repeated denials of any bout fixing. The e-mails even apparently go so far as to list amounts to be paid and bank account numbers, as well as how exactly the fixed bouts would unfold in the ring.

Over the years, various allegations have come out regarding match fixing and the JSA has successfully sued publishers responsible for printing such stories. The JSA will likely try to claim that these match fixing e-mails are totally different and very recent development.

One example of the authors’ use of economic theory involves demonstrating the existence of cheating among sumo wrestlers. In a sumo tournament, all wrestlers in the top division compete in 15 matches and face demotion if they do not win at least eight of them. The sumo community is very close-knit, and the wrestlers at the top levels tend to know each other well. The authors looked at the final match, and considered the case of a wrestler with seven wins, seven losses, and one fight to go, fighting against an 8-6 wrestler. Statistically, the 7-7 wrestler should have a slightly below even chance, since the 8-6 wrestler is slightly better. However, the 7-7 wrestler actually wins around 80% of the time. Levitt uses this statistic and other data gleaned from sumo wrestling matches, along with the effect that allegations of corruption have on match results, to conclude that those who already have 8 wins collude with those who are 7-7 and let them win, since they have already secured their position for the following tournament.